You really need to think of retail and classic as two separate things. Two different existences, two different dimensions/universes.
Everything in retail has it’s value based on the history of the game. If you allow classic to change things in retail you are adjusting the values of rewards/achievements. You’re going back in time and giving yourself things that potentially no longer exist.
It’s a different game. It’s a different everything. Retail and Classic should never be linked.